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Physics Unit One

Physics Unit One. Motion. Motion. Any change in the position of an object. Can be completely described with speed and direction. The distance an object travels per unit of time. s = d / t Units - any distance over any time. Ex. m/s, km/hr, cm/s, etc…. Speed PLUS direction.

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Physics Unit One

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  1. Physics Unit One Motion

  2. Motion • Any change in the position of an object. • Can be completely described with speed and direction.

  3. The distance an object travels per unit of time. s = d / t Units - any distance over any time. Ex. m/s, km/hr, cm/s, etc… Speed PLUS direction. A vector quantity (magnitude + direction) v = d / t, direction Units – any distance over any time, plus, direction. Ex. 6.5 cm/s, due north Speed vs. Velocity

  4. 5-Step Method for Solving Problems A cat can run 5.0 meters in 3.25 seconds. What is the cat’s average speed? d = 5.0 m t = 3.25 s s = d / t s = 5.0m / 3.25s s = 1.54 m/s

  5. Velocity Sample Problem • A tennis ball flies off the end of a racket and travels 10.0 meters in 0.95s. What is the velocity of the tennis ball? d = 10.0 m t = 0.95s v = d / t v = 10.0m / 0.95s v = 10.53 m/s, across the net

  6. d vs. t graphs • Graph the motion • use the slope to interpret the relationship between the variables (d & t) ΔY rise d = = = = Slope Speed run ΔX t *steeper the slope  faster the speed *more gentle the slope  slower the speed

  7. When interpreting the motion answer: • As time goes by, distance (d  or ) • The line shows relationship (constant or changing) d d d d t t t t • Moving forward (d) • No motion (d stays same) • Moving backward (d) • Moving forward (d) • Constant speed (straight) • Constant speed (straight) • Constant speed (straight) • Changing speed (curved) • 0 m/s • positive acceleration

  8. d d d t t t • Moving forward (d) • Moving backward (d) • Moving backward (d) • changing speed (curved) • changing speed (curved) • changing speed (curved) • (-) acceleration • (-) acceleration • (+) acceleration

  9. AB • Move forward • Constant speed • ΔY 10m 1m/s = = 10s ΔX BC • At rest • Constant speed • 0m/s

  10. CD • Moving backward • Constant speed • ΔY 5m 1m/s = = ΔX 5s DE • Moving forward • Changing speed • (+) acceleration

  11. EF • Moving backward • Constant speed • ΔY 25m 5m/s = = ΔX 5s FG • Moving forward • Constant speed • ΔY 10m 2m/s = = ΔX 5s GH • Moving forward • Constant speed 12.5m • ΔY = 1m/s = ΔX 12.5s

  12. Which line had the fastest speed? • EF • Steepest slope Distance increases? • Moving forward Distance decreases? • Moving backward Straight line? • Constant speed Curved line? • Changing speed d vs. t graph shows? • Speed and direction

  13. Unit 1 Physics Acceleration

  14. Acceleration • Any change in velocity (speed or direction) of an object a = vf - vi t a = acceleration vf = final velocity vi = initial velocity t = time

  15. Example:A runner increases her speed from 3m/s to 10m/s in 2 seconds. Calculate her rate of acceleration. vf = 10m/s vi = 3m/s t = 2s a = vf - vi t a = 7m/s 2s a = 10m/s - 3m/s 2s a = 3.5m/s2 She gets 3.5m/s faster every second. 0s = 3m/s 1s = 6.5m/s 2s = 10m/s

  16. a = 0km/hr - 88km/hr 4s Example: A car goes from 88km/hr to stopped in 4s. vf = 0km/hr vi = 88km/hr t = 4s a = -22km/hr s a = -88km/hr 4s a = vf - vi t The car gets 22km/hr slower every second. 0s = 88km/hr 2s = 44km/hr 4s = 0km/hr 1s = 66km/hr 3s = 22km/hr

  17. When interpreting the motion answer: • As time goes by, velocity (v  or ) • The line shows relationship (constant or changing) v v v v t t t t • Constant • acceleration • 0m/s2 • Constant • negative • acceleration • Constant • positive • acceleration • Changing • positive • acceleration • Constant speed

  18. v v v t t t • Changing • positive • acceleration • Changing • negative • acceleration • Changing • negative • acceleration

  19. AB • Constant (+) acceleration 10m/s - 0m/s = 10s 10m/s 1m/s2 = 10s BC • Constant speed • 10m/s • Constant acceleration 0m/s2

  20. CD • Constant (-) acceleration 5m/s - 10m/s = 5s -5m/s -1m/s2 = 5s DE • Changing (+) acceleration

  21. EF • Constant (-) acceleration 0m/s - 25m/s = 5s -25m/s -5m/s2 = 5s FG • Constant (+) acceleration 10m/s - 0m/s = 5s 10m/s 2m/s2 = 5s

  22. GH • Constant (+) acceleration 22.5m/s - 10m/s = 12.5s 12.5m/s 1m/s2 = 12.5s

  23. The car accelerated, stayed at the same speed, slowed down for light, light turns & quickly accelerates, slams on the brakes to stop for red light, quickly accelerates, continues at slower acceleration

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